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Introduction C 3, C 4 and CAM photosynthesis are the three types of photosynthesis in green plants. C 3 photosynthesis is the photosynthesis we have learned about in class. C 4 and CAM photosynthesis are adaptations to arid conditions.

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C 3 Photosynthesis C 3 is so called because the first compound made when carbon dioxide is fixed from the atmosphere has three carbons (PGAL). Stomata are open during the day. RuBisco is the enzyme involved in carbon fixation.

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C 3 Photosynthesis Photosynthesis takes place throughout the leaf. Most plants are C3 because it requires fewer enzymes and less specialized machinery than C4 and CAM photosynthesis. It is the most efficient form of photosynthesis under normal light intensity, lower temperature and normal moisture.

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C 4 Photosynthesis Called C 4 because carbon dioxide is fixed into a four carbon compound. Stomata open during the day. Dark Reactions take place in inner cells called Kranz Anatomy.

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C 4 Photosynthesis Uses the enzyme PEP carboxylase to fix carbon dioxide into a four carbon compound (usually malic acid) and then delivers it to RuBisCO to provide carbon dioxide and continue photosynthesis similar to the C 3 pathway.

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C 4 Photosynthesis This works faster than C 3 photosynthesis under high light intensity and high temperature because it delivers CO 2 directly to RuBisCO thereby maximizing carbohydrate formation and preventing product loss due to photorespiration.

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Photorespiration Definition Photorespiration is a process in plant metabolism by which RuBP (a sugar) has oxygen added to it by RuBisCO, instead of carbon dioxide during normal photosynthesis. This process reduces efficiency of photosynthesis in C3 plants. Oxygen acts as a competitive inhibitor.

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C 4 Photosynthesis It is also more efficient in terms of water use because PEP carboxylase brings in CO 2 faster and therefore does not need to keep the stomata open for as long, thereby minimizing water loss. C 4 photosynthesis is common in plants that grow mainly during the intense heat of summer in North America (i.e. Corn).

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CAM Photosynthesis Crassulacean acid metabolism CAM) photosynthesis is another adaptation for plants that are in arid conditions. Stomata are closed during the day and open at night to reduce water loss through transpiration.

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CAM Photosynthesis These plants fix carbon dioxide into vacuoles during the night and incorporate it into malic acid similar to the C4 pathway. During the day, the malic acid transfers carbon dioxide to RuBisCO and carbohydrate is made.

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CAM Photosynthesis CAM plants often have thick, reduced leaves with a low SA to V ratio; thick cuticle; and stomata sunken into pits. Some store water in vacuoles (succulent plants). CAM plants can also be recognized as plants whose leaves have an increasing sour taste during the night yet become sweeter-tasting during the day. This is due to malic acid stored in the vacuoles of the plants' cells during the night and then used up during the day. That is why we let pineapple ripen before eating!

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CAM Photosynthesis CAM plants can “CAM-idle” which allows them to keep their stomata closed at all times during extremely arid conditions and therefore any oxygen they give off in photosynthesis is immediately used in cellular respiration and vice versa. This allows the plant to survive dry periods and recover very quickly when water returns.

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CAM vs. C 4 Photosynthesis Similarities Differences Both are a response to arid conditions. Both use water more efficiently than C3 plants. Both minimize the amount of photorespiration by proving carbon dioxide directly to RuBisCO. CAM plants provide CO 2 temporally (stockpile it at night and provide it during the day) whereas C4 plants provide CO 2 spatially (take it from the outer cells and provide it to the inner Kranz Anatomy). C4 plants require special Krantz Anatomy. C4 plants have stomata open during the day while CAM plants have stomata open at night.